The present invention relates to a storage apparatus and a control method thereof, and more particularly relates to a difference bit map management method, storage apparatus, and information processing system for recording a difference between volumes in the storage apparatus.
In the past, as to a method for managing a difference between volumes in a storage apparatus by using a bit map, the storage apparatus has a bit map on an internal memory and, a host processor has specified which one is a block having been written after an acquisition of a snapshot for performing an acquisition of difference data with respect to a certain volume as disclosed in the patent reference 1, for example. Furthermore, each bit in the bit map thereof had a correspondence of 1:1 to the block according to the patent reference 1.
In addition, in a method for managing a cache memory in this storage apparatus by using a directory, a cache directory (a directory to manage the cache memory) had information for controlling an area on the cache memory.
[Patent reference 1] U.S. Pat. No. 6,618,794 Specifications
However, in the bit map management method described in the above-mentioned patent reference 1, it is necessary to prepare a memory area for a bit map to record a difference, which manages renewal with respect to data stored in a logical volume at a certain time point (hereinafter, referred to as “difference bit map”) in the storage apparatus to the extent proportional to a size of a volume intended to record the difference. Due to this reason, there has been such an inconvenience that the more the total amount of volumes intended to record the difference increases, the more the memory becomes necessary.